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Author Topic: Bob's H.M.S. Polyphemus  (Read 209721 times)

steve pickstock

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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #200 on: December 14, 2012, 01:07:25 pm »

As the idea is only about altering the waterline of Polyphemus would some blue foam blocks in the flotation tanks - effectively reducing the amount of water into the f/tank initially - do any good?
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Snowwolflair

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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #201 on: December 14, 2012, 01:16:03 pm »

Submarine dive bladders inside the spaces connected directly to the pump.
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Bob K

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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #202 on: December 14, 2012, 01:22:52 pm »

Unfortunately adding anything inside the ballast tanks is no longer an option as they are now both fully sealed in.

Hopefully part-pressurising them from the 12V air pump will help.  I will try that after I have sorted out the remaining slow leaks.
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HMS Skirmisher (1905), HMS Amazon (1906), HMS K9 (1915), Type 212A (2002), HMS Polyphemus (1881), Descartes (1897), Iggle Piggle boat (CBBC), HMS Royal Marine (1943), HMS Marshall Soult, HMS Agincourt (1912)

Subculture

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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #203 on: December 14, 2012, 01:28:01 pm »

Looking at the pictures, it appears you've been very sparing with the sikaflex. You need a nice thick bead to get the best out of this stuff. Think along the lines of how you'd caulk your bathtub.

Also a third of the tank filling sounds a lot to me- think you have an air leak in the tanks somewhere.

derekwarner

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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #204 on: December 14, 2012, 02:01:54 pm »

Hullo Bob....watching from afar [22,000km]...... :embarrassed: water & air in compression certainly don't mix....it is the air pocket that is the issue & the result is the physical instability of the water sloshing around that can un predicitably alter the vessel's trim or heel......  >>:-( ......I would take counsel from member Subculture here .....
Do you remember an older family member detecting a leak in a motor vehicle tyre tube?..... by immersing the infated tube in a water container %% .......
I think the family home bathroom [bath] is going to be fully booked for some time to come ........good luck.......Derek
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Derek Warner

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Bob K

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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #205 on: December 14, 2012, 02:05:42 pm »

OK Subculture.  I was aiming for a balance between effective and neat with so much clear Lexan used its like a display case inside.  At least clear Lexan allows to me to see what is going on inside.

I have almost used up one tube of 221 due to combined length of joints, and have now ordered another.
 
Derek:  I do have sets of baffles fitted inside the tanks to reduce sloshing.
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derekwarner

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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #206 on: December 14, 2012, 02:43:07 pm »

 :o  ....Bob...baffels will only retard the rate of sloshing ......if you have an air pocket it can only be compressed by the pressure generated by the pump  >>:-(  You could consider low pressure check valves to displace the air pocket .....Derek
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Derek Warner

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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #207 on: December 14, 2012, 04:57:33 pm »

This type of ballast system should be run completely empty or completely full. If you run with a partially filled tank, then you will most likely experienced instability problems, especially if the tanks are long and thin.

Differing water densities (affected by temperature and mineral content) will affect the trim of the vessel, but only by about 1-2% of the boats overall displacment, and that can easily be taken up by a small amount of lead weight placed on the vessels C.G, which can be added or subtracted as required.

Bob K

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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #208 on: December 14, 2012, 07:22:52 pm »

This type of ballast system should be run completely empty or completely full. If you run with a partially filled tank, then you will most likely experienced instability problems, especially if the tanks are long and thin.

The design intent was always to run the tanks either full or empty, to recreate either trimmed down attack-mode or higher riding for when the pond is not so calm.  The two 1.2 litre tanks are open vented with slots at their bases.  Air is either released via ball valves, or forced in via a 12V air pump, both at the top. 
 
Air tubes will terminate near the top of the funnel which will have two concentric tubes, the inner for the smoke to rise from, the large outer for air inlet for the Mister.
 
I am indebted to expert submariners on Mayhem as the principles involved are akin to scratch building a submarine, hence the subject title.  I still have much to learn in this field.   %%
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HMS Skirmisher (1905), HMS Amazon (1906), HMS K9 (1915), Type 212A (2002), HMS Polyphemus (1881), Descartes (1897), Iggle Piggle boat (CBBC), HMS Royal Marine (1943), HMS Marshall Soult, HMS Agincourt (1912)

Subculture

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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #209 on: December 14, 2012, 07:52:39 pm »

You shouldn't have any difficulty then. The system you have is basically a large snort system, minus the gas back-up, which is unecessary as you're not going fully under (you hope!).

In ballast system terms, things don't get any simpler than this. If you have problems tracking down very small leaks, I recommend you try the old gas fitters trick of mixing up some dishwashing liquid with water, and brush that around all the seams, pipes etc. to do with the tanks. Place it in the drink, and any leaks should make themselves apparent by blowing bubbles!

Bob K

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Re: H.M.S. Polyphemus (1881), more sealant
« Reply #210 on: December 20, 2012, 12:00:11 pm »


More sealant

After the initial bath test I ordered another tube of white Silkaflex 212, this time applying more generously with the mastic gun around all the compartment joints. 
I had hoped for a much neater job, but not at the risk of inadvertently recreating a rare and intricately carved Glug-Glug Box. 
( See http://www.hitrecord.org/records/313435 )

Before adding more mastic I first applied Slo-Zap thick CA along the edges of the inter compartment hardwood reinforcers which had previously been epoxied.

One day to set off, then refill the bath.

Another bath test

Bare hull floated in bath, no apparent leaks. Left hull a couple of hours to make sure, no problems.  Odd thing is that when you heel it over to one side that ballast chamber becomes lower in the water, fills more, and stays at that angle of list when you let go.   Not self righting.

Adding the mass of batteries etc this effect is much more pronounced, almost to the point of risking capsize. 
I may need an extended keel ?
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HMS Skirmisher (1905), HMS Amazon (1906), HMS K9 (1915), Type 212A (2002), HMS Polyphemus (1881), Descartes (1897), Iggle Piggle boat (CBBC), HMS Royal Marine (1943), HMS Marshall Soult, HMS Agincourt (1912)

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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #211 on: December 20, 2012, 01:49:57 pm »

This design of boat has much less powerful self-righting moment than a more conventional boat owing to the reduced buoyancy.

Looking at your layout, you have a lot of heavy objects quite high up in the hull.

Bob K

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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #212 on: December 20, 2012, 02:38:02 pm »

This design of boat has much less powerful self-righting moment than a more conventional boat owing to the reduced buoyancy.

Looking at your layout, you have a lot of heavy objects quite high up in the hull.

I agree.  The section amidships is nowhere near as straight sided and flat bottomed as a more conventional warship for fitting electrics.  Also the ends are rather narrow not providing much bouyancy.  The mister is bulky but not heavy, and the motors are almost down in the base of the hull.  The air pump sits in the keel curve.
I may need to go to a smaller 6V battery, whose width defines how low it can go, and use more lead in the keel spaces.
 

 
Interesting.  At least it floats !
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HMS Skirmisher (1905), HMS Amazon (1906), HMS K9 (1915), Type 212A (2002), HMS Polyphemus (1881), Descartes (1897), Iggle Piggle boat (CBBC), HMS Royal Marine (1943), HMS Marshall Soult, HMS Agincourt (1912)

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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #213 on: December 21, 2012, 12:39:50 am »

All fascinating stuff for me - great build thread Bob.  :-))

Dave
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Subculture

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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #214 on: December 21, 2012, 07:19:31 am »

I'm still concerned about the ballast tanks filling up. The air inside should provide a 'spring' against that, Even if you have the thing fully underwater, you should have no more than a tenth of a PSI pushing against the air inside, which is close to nothing.

Have you got the tanks fully plugged when testing??

Bob K

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Re: H.M.S. Polyphemus (1881), pressure tight ?
« Reply #215 on: December 21, 2012, 08:58:33 am »


 
Pressure tight ?
 
Everything appears watertight.  Water level does not come up as much in the tanks.  Washing up liquid test did not show air leaks around the underdeck to hull joins.  The four 4mm brass tube stubs for ballast air control tubes have been plugged with well kneaded Blu-Tack.  I would have expected more resistance to listing with the retained air volumes acting as buoyancy floats.
 
What I may now have to search for is whether the ballast tanks are air pressure tight, but that will involve removing both servos and going for full depth immersion.
 
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HMS Skirmisher (1905), HMS Amazon (1906), HMS K9 (1915), Type 212A (2002), HMS Polyphemus (1881), Descartes (1897), Iggle Piggle boat (CBBC), HMS Royal Marine (1943), HMS Marshall Soult, HMS Agincourt (1912)

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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #216 on: December 21, 2012, 09:19:58 am »

Looking at the pictures, the vents look like they're right at the bottom of the tanks, which is correct.

You'll only need a minute leak to create a problem.

derekwarner

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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #217 on: December 21, 2012, 09:29:34 am »

Bob....please corect me if my thoughts are not on track  :((
 
If your ballast tanks are not self bleeding for air ....when you commence to fill/flood/pump water into the tank you are attempting to compress the entrapped air at 1 atmosphere or approx 14.7 PSI
 
A simple test would be to ballast the hull to the required depth by adding lead material ...... then weight the lead....you can simply then repeat with water & base the water as 1 kg/litre
 
Re-reading the communication string below suggests that a design concept is not quite right...... :embarrassed:  ....Derek
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Derek Warner

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Bob K

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Re: H.M.S. Polyphemus (1881), Subs 101
« Reply #218 on: December 21, 2012, 12:30:39 pm »


Submarines 101

101, to use an American college expression.  Although I have built boats before, in this field I am learning the hard way.  One evident design weakness is in the considerable mileage of joints that need to be completely airtight as well as watertight.

Derek:  Each ballast chamber is measured at 1.2 L, making approx 2.4 Kg of ballast when both full.  I have had it floating with principle heavy items installed. 
It floats level and not too far off expected waterline.  Air tubes at the tank tops are temporarily sealed off.

As Subculture pointed out even the tiniest air leaks can be fatal.  It should be an almost sealed system unless air is either valve released or pumped in.  I should be able to push the hull almost under without levels in the tanks increasing appreciably.

Total submergence test

Servos removed.  Seams lathered in washing up liquid, then gradually forcing the hull under water.
I found two small air leaks on the starboard side where the frame meets the underdeck, but none apparent on the port side.  I need to re-caulk the entire length of the tank side frames at the top joints, which are now inside the compartments so I will have to work through the access hatch openings.

 

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Shipmate60

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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #219 on: December 21, 2012, 01:31:50 pm »

Bob,
One of my concerns is the longevity of the system.
With dissimilar materials and the need for the tanks to remain 100% watertight.

Bob
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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #220 on: December 21, 2012, 02:16:45 pm »

Because Bob has used a flexible adhesive, which is very strong, he shouldn't get any issues at all. The bond permits a certain amount of expansion and contraction, unlike if he'd used a resin type adhesive e.g epoxy or polyester. But as I pointed out earlier, you need to ensure a good bead of it to work well.

Bob K

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Re: H.M.S. Polyphemus (1881), Icing the Cake
« Reply #221 on: December 31, 2012, 01:54:09 pm »


Icing the Cake

Adding loads more mastic sealant will hopefully get this complex assembly finally airtight, even if it does end up looking more like a royal icing Christmas cake than the neat job I started off with.  The lower joints all seem watertight, but access to joints on the undersides of the clear Lexan under deck is beyond the reach of a standard mastic nozzle.

Icing Nozzle

On the cake decorating theme I made up a curved icing nozzle extension from alloy tube secured with a reinforced joint using layers of high strength epoxy. 



I had to get an all-metal mastic gun as the pressure snapped the plastic trigger handle.

The nozzle did just about take the gun pressure until almost the end.  The aim was to squeeze the mastic direct up under the joint corners and in between the nutserts.  Looks reasonable, even if now very messy.  I could have used non-clear material for the under deck.  Sad.



Back to the Test Tank

If this isn't watertight and airtight then . . . .   >>:-(

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HMS Skirmisher (1905), HMS Amazon (1906), HMS K9 (1915), Type 212A (2002), HMS Polyphemus (1881), Descartes (1897), Iggle Piggle boat (CBBC), HMS Royal Marine (1943), HMS Marshall Soult, HMS Agincourt (1912)

Bob K

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Re: H.M.S. Polyphemus (1881), Back in the Bath
« Reply #222 on: January 01, 2013, 10:58:03 pm »


Back in the Bath

After News Years Eve re-caulking mastic with my special icing nozzle it was time to re-test the air and water integrity of the many metres of joints, particularly those around the two ballast chambers.

The full push down forced sinking test revealed a couple of small air leaks near the stern end of the tank plates, so a thorough dry down followed by a third layer of mastic over those areas, which were now half an inch thick. 

Finally however no further tiny air bubble streams were seen and it appears that the chambers are at last airtight.  When dried off again and pushed down to full draught waterline less than 5 mm water was in the bottom of each tank. 

Next test will be adding the principle heavy items, opening up the tank air vents and checking where the waterline will come to.
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Subculture

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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #223 on: January 01, 2013, 11:34:48 pm »

There you go, I said you'd get a result once the thing was gas tight.

Now, next time you use sikaflex, you might want to try the old trick of masking off either side of where you want the bead, apply the caulking then use a wet finger to form the bead into a pleasant bead, remove tape and you should have a very neat seam.

Bob K

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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #224 on: January 01, 2013, 11:54:52 pm »

Thank you Subculture:  With hindsight, if I had known then etc, I would have built the ballast tanks separately and sealed them to the hull using less joints.  Compartments in between only need to be reasonably watertight.  Where I had arrived at precluded masking tape as the key joints were all between the under-deck, hull and side frames.  Even with a wet finger this is darn sticky stuff to work with.
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HMS Skirmisher (1905), HMS Amazon (1906), HMS K9 (1915), Type 212A (2002), HMS Polyphemus (1881), Descartes (1897), Iggle Piggle boat (CBBC), HMS Royal Marine (1943), HMS Marshall Soult, HMS Agincourt (1912)
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